Wearable medical device usage by healthcare consumers has almost quadrupled in the past four years. It is up from nine percent in 2014 to 33 percent today, according to a survey released by Accenture. And the global market for these devices is projected to reach $12.1 billion by 2021, according to a study conducted by Markets and Markets, with the United States representing the largest market worldwide.

These products increasingly rely on wireless communications to transmit and receive data from controllers or smartphones. Those wireless technologies include something familiar to those who use consumer electronics, Bluetooth. “Bluetooth is a logical choice,” said Anthony Ng, senior engineering manager, Diabetes R&D at Medtronic. “Bluetooth goes well with a lot of applications with wearable devices outside the body,” he told MD+DI. Ng will present "Challenges and Trends of Wireless Technologies for Wearable Medical Devices" on December 5 at BIOMEDevice San Jose.

However, the human body itself poses some challenges when designing wearable devices. “The problem is the human body’s effect on radio frequency,” Ng said. “When you have multiple wearable devices, then you need something that can go full body. RF frequencies of Bluetooth and Wi-Fi are lousy going through the body and maintaining the reliable link is one of the major challenges.”

So, part of the industry may be gearing toward more human body-friendly technologies such as adaptive radiation pattern, mesh network, or advanced near-field magnetic induction (NFMI). NFMI is a short-range wireless physical layer that communicates by coupling a tight, low-power, nonpropagating magnetic field between devices. The concept is for a transmitter coil in one device to modulate a magnetic field that is measured by means of a receiver coil in another device.

Ng said other challenges for designers include stability, power, and how to foolproof link security, especially for Class 2 and Class 3 medical devices. “Anything where patient safety is involved,” he explained.

“Also, there is limited power source that you can store on the device, so other things to consider are whether to use a rechargeable battery or a disposable battery. How many times you charge the battery,” he continued. But the bottom line is that reliability of the link is critical, Ng stressed.

These are just a few examples of technologies and their capabilities, as well as limitations, for engineers of wearable medical devices, said Ng. “They all have their pros and cons, such as reliability, security, and so forth.” His presentation will go into more detail about key design and implementation challenges to overcome.